This invention relates to voice communication systems, and more particularly to methods and apparatus for detecting the occurrence of voice information in a telephone-type signal.
Automated voice messaging systems sometimes require the ability to automatically place a telephone call, and when that call is answered, to transmit a previously recorded message to the person answering the call. For example, a voice processing system such as a voice mail system may receive and record messages for a subscriber or user at any time during the day. At some predetermined subsequent time convenient for the user, if any messages have been received, the system may call that user to tell him or her that messages have been received and to play back those messages if the user elects to hear them. For example, when the automatically placed call is answered, the system may first transmit a prerecorded standard announcement identifying the system to the user and stating that the user has a specified number of new messages which can be audited. The user then operates the buttons on his or her DTMF ("Touch-Tone") telephone to tell the system whether or not to play the messages and/or to cause the system to perform other tasks.
A problem with such systems is to enable the system to know when to begin transmitting the initial announcement after the automatically placed call has been answered. Prior systems have begun the initial announcement a predetermined time interval after the system detects that the ringing signal has stopped. This is a relatively imprecise and unsatisfactory way to commence the announcement. For example, if the call is answered immediately after a ring and the person answering moves the telephone handset quickly to his or her ear, there may be a disconcertingly long silence before the initial announcement begins. On the other hand, if the call is answered just before a ring would otherwise have occurred and the person answering moves the handset relatively slowly to his or her ear, the initial announcement may begin before the person answering can hear it.
A better technique would be for the system to begin the initial announcement after detecting that the person answering the call has spoken (e.g., said "hello") into his or her handset.
Accordingly, it is an object of this invention to improve voice communication systems of the type which automatically place a telephone call and make a voice announcement after that call is answered by causing such systems to detect a voice response to the call and to begin the voice announcement after that voice response has been detected.
The signals on telephone lines are often quite complex and noisy, and it can therefore be difficult to determine whether or not such a signal includes voice information.
It is therefore another object of this invention to provide improved methods and apparatus for determining whether or not the signal on a telephone line includes voice information.